lkml.org 
[lkml]   [2019]   [Jan]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH RFC 00/24] userfaultfd: write protection support
    From
    Date
    On 21.01.19 08:56, Peter Xu wrote:
    > Hi,
    >
    > This series implements initial write protection support for
    > userfaultfd. Currently both shmem and hugetlbfs are not supported
    > yet, but only anonymous memory.
    >
    > To be simple, either "userfaultfd-wp" or "uffd-wp" might be used in
    > later paragraphs.
    >
    > The whole series can also be found at:
    >
    > https://github.com/xzpeter/linux/tree/uffd-wp-merged
    >
    > Any comment would be greatly welcomed. Thanks.
    >
    > Overview
    > ====================
    >
    > The uffd-wp work was initialized by Shaohua Li [1], and later
    > continued by Andrea [2]. This series is based upon Andrea's latest
    > userfaultfd tree, and it is a continuous works from both Shaohua and
    > Andrea. Many of the follow up ideas come from Andrea too.
    >
    > Besides the old MISSING register mode of userfaultfd, the new uffd-wp
    > support provides another alternative register mode called
    > UFFDIO_REGISTER_MODE_WP that can be used to listen to not only missing
    > page faults but also write protection page faults, or even they can be
    > registered together. At the same time, the new feature also provides
    > a new userfaultfd ioctl called UFFDIO_WRITEPROTECT which allows the
    > userspace to write protect a range or memory or fixup write permission
    > of faulted pages.
    >
    > Please refer to the document patch "userfaultfd: wp:
    > UFFDIO_REGISTER_MODE_WP documentation update" for more information on
    > the new interface and what it can do.
    >
    > The major workflow of an uffd-wp program should be:
    >
    > 1. Register a memory region with WP mode using UFFDIO_REGISTER_MODE_WP
    >
    > 2. Write protect part of the whole registered region using
    > UFFDIO_WRITEPROTECT, passing in UFFDIO_WRITEPROTECT_MODE_WP to
    > show that we want to write protect the range.
    >
    > 3. Start a working thread that modifies the protected pages,
    > meanwhile listening to UFFD messages.
    >
    > 4. When a write is detected upon the protected range, page fault
    > happens, a UFFD message will be generated and reported to the
    > page fault handling thread
    >
    > 5. The page fault handler thread resolves the page fault using the
    > new UFFDIO_WRITEPROTECT ioctl, but this time passing in
    > !UFFDIO_WRITEPROTECT_MODE_WP instead showing that we want to
    > recover the write permission. Before this operation, the fault
    > handler thread can do anything it wants, e.g., dumps the page to
    > a persistent storage.
    >
    > 6. The worker thread will continue running with the correctly
    > applied write permission from step 5.
    >
    > Currently there are already two projects that are based on this new
    > userfaultfd feature.
    >
    > QEMU Live Snapshot: The project provides a way to allow the QEMU
    > hypervisor to take snapshot of VMs without
    > stopping the VM [3].
    >
    > LLNL umap library: The project provides a mmap-like interface and
    > "allow to have an application specific buffer of
    > pages cached from a large file, i.e. out-of-core
    > execution using memory map" [4][5].
    >
    > Before posting the patchset, this series was smoke tested against QEMU
    > live snapshot and the LLNL umap library (by doing parallel quicksort
    > using 128 sorting threads + 80 uffd servicing threads). My sincere
    > thanks to Marty Mcfadden and Denis Plotnikov for the help along the
    > way.
    >
    > Implementation
    > ==============
    >
    > Patch 1-4: The whole uffd-wp requires the kernel page fault path to
    > take more than one retries. In the previous works starting
    > from Shaohua, a new fault flag FAULT_FLAG_ALLOW_UFFD_RETRY
    > was introduced for this [6]. However in this series we have
    > dropped that patch, instead the whole work is based on the
    > recent series "[PATCH RFC v3 0/4] mm: some enhancements to
    > the page fault mechanism" [7] which removes the assuption
    > that VM_FAULT_RETRY can only happen once. This four
    > patches are identital patches but picked up here. Please
    > refer to the cover letter [7] for more information. More
    > discussion upstream shows that this work could even benefit
    > existing use case [8] so please help justify whether
    > patches 1-4 can be consider to be accepted even earlier
    > than the rest of the series.
    >
    > Patch 5-21: Implements the uffd-wp logic. To avoid collision with
    > existing write protections (e.g., an private anonymous
    > page can be write protected if it was shared between
    > multiple processes), a new PTE bit (_PAGE_UFFD_WP) was
    > introduced to explicitly mark a PTE as userfault
    > write-protected. A similar bit was also used in the
    > swap/migration entry (_PAGE_SWP_UFFD_WP) to make sure
    > even if the pages were swapped or migrated, the uffd-wp
    > tracking information won't be lost. When resolving a
    > page fault, we'll do a page copy before hand if the page
    > was COWed to make sure we won't corrupt any shared
    > pages. Etc. Please see separated patches for more
    > details.
    >
    > Patch 22: Documentation update for uffd-wp
    >
    > Patch 23,24: Uffd-wp selftests
    >
    > TODO
    > =============
    >
    > - hugetlbfs/shmem support
    > - performance
    > - more architectures
    > - ...
    >
    > References
    > ==========
    >
    > [1] https://lwn.net/Articles/666187/
    > [2] https://git.kernel.org/pub/scm/linux/kernel/git/andrea/aa.git/log/?h=userfault
    > [3] https://github.com/denis-plotnikov/qemu/commits/background-snapshot-kvm
    > [4] https://github.com/LLNL/umap
    > [5] https://llnl-umap.readthedocs.io/en/develop/
    > [6] https://git.kernel.org/pub/scm/linux/kernel/git/andrea/aa.git/commit/?h=userfault&id=b245ecf6cf59156966f3da6e6b674f6695a5ffa5
    > [7] https://lkml.org/lkml/2018/11/21/370
    > [8] https://lkml.org/lkml/2018/12/30/64
    >
    > Andrea Arcangeli (5):
    > userfaultfd: wp: add the writeprotect API to userfaultfd ioctl
    > userfaultfd: wp: hook userfault handler to write protection fault
    > userfaultfd: wp: add WP pagetable tracking to x86
    > userfaultfd: wp: userfaultfd_pte/huge_pmd_wp() helpers
    > userfaultfd: wp: add UFFDIO_COPY_MODE_WP
    >
    > Martin Cracauer (1):
    > userfaultfd: wp: UFFDIO_REGISTER_MODE_WP documentation update
    >
    > Peter Xu (15):
    > mm: gup: rename "nonblocking" to "locked" where proper
    > mm: userfault: return VM_FAULT_RETRY on signals
    > mm: allow VM_FAULT_RETRY for multiple times
    > mm: gup: allow VM_FAULT_RETRY for multiple times
    > mm: merge parameters for change_protection()
    > userfaultfd: wp: apply _PAGE_UFFD_WP bit
    > mm: export wp_page_copy()
    > userfaultfd: wp: handle COW properly for uffd-wp
    > userfaultfd: wp: drop _PAGE_UFFD_WP properly when fork
    > userfaultfd: wp: add pmd_swp_*uffd_wp() helpers
    > userfaultfd: wp: support swap and page migration
    > userfaultfd: wp: don't wake up when doing write protect
    > khugepaged: skip collapse if uffd-wp detected
    > userfaultfd: selftests: refactor statistics
    > userfaultfd: selftests: add write-protect test
    >
    > Shaohua Li (3):
    > userfaultfd: wp: add helper for writeprotect check
    > userfaultfd: wp: support write protection for userfault vma range
    > userfaultfd: wp: enabled write protection in userfaultfd API
    >
    > Documentation/admin-guide/mm/userfaultfd.rst | 51 +++++
    > arch/alpha/mm/fault.c | 4 +-
    > arch/arc/mm/fault.c | 12 +-
    > arch/arm/mm/fault.c | 17 +-
    > arch/arm64/mm/fault.c | 11 +-
    > arch/hexagon/mm/vm_fault.c | 3 +-
    > arch/ia64/mm/fault.c | 3 +-
    > arch/m68k/mm/fault.c | 5 +-
    > arch/microblaze/mm/fault.c | 3 +-
    > arch/mips/mm/fault.c | 3 +-
    > arch/nds32/mm/fault.c | 7 +-
    > arch/nios2/mm/fault.c | 5 +-
    > arch/openrisc/mm/fault.c | 3 +-
    > arch/parisc/mm/fault.c | 4 +-
    > arch/powerpc/mm/fault.c | 9 +-
    > arch/riscv/mm/fault.c | 9 +-
    > arch/s390/mm/fault.c | 14 +-
    > arch/sh/mm/fault.c | 5 +-
    > arch/sparc/mm/fault_32.c | 4 +-
    > arch/sparc/mm/fault_64.c | 4 +-
    > arch/um/kernel/trap.c | 6 +-
    > arch/unicore32/mm/fault.c | 10 +-
    > arch/x86/Kconfig | 1 +
    > arch/x86/include/asm/pgtable.h | 67 ++++++
    > arch/x86/include/asm/pgtable_64.h | 8 +-
    > arch/x86/include/asm/pgtable_types.h | 11 +-
    > arch/x86/mm/fault.c | 13 +-
    > arch/xtensa/mm/fault.c | 4 +-
    > fs/userfaultfd.c | 110 +++++----
    > include/asm-generic/pgtable.h | 1 +
    > include/asm-generic/pgtable_uffd.h | 66 ++++++
    > include/linux/huge_mm.h | 2 +-
    > include/linux/mm.h | 21 +-
    > include/linux/swapops.h | 2 +
    > include/linux/userfaultfd_k.h | 41 +++-
    > include/trace/events/huge_memory.h | 1 +
    > include/uapi/linux/userfaultfd.h | 28 ++-
    > init/Kconfig | 5 +
    > mm/gup.c | 61 ++---
    > mm/huge_memory.c | 28 ++-
    > mm/hugetlb.c | 8 +-
    > mm/khugepaged.c | 23 ++
    > mm/memory.c | 28 ++-
    > mm/mempolicy.c | 2 +-
    > mm/migrate.c | 7 +
    > mm/mprotect.c | 99 +++++++--
    > mm/rmap.c | 6 +
    > mm/userfaultfd.c | 92 +++++++-
    > tools/testing/selftests/vm/userfaultfd.c | 222 ++++++++++++++-----
    > 49 files changed, 898 insertions(+), 251 deletions(-)
    > create mode 100644 include/asm-generic/pgtable_uffd.h
    >

    Does this series fix the "false positives" case I experienced on early
    prototypes of uffd-wp? (getting notified about a write access although
    it was not a write access?)

    --

    Thanks,

    David / dhildenb

    \
     
     \ /
      Last update: 2019-01-21 15:34    [W:2.695 / U:0.012 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site